1. Field of the Invention
The present invention relates to an imaging apparatus, an imaging method and a recording medium capable of minimizing a time (hereinafter referred to as release time lag) until an actual exposure is initiated, after a release shutter button is pressed.
2. Description of the Prior Art
Generally, means for controlling an exposure time of an imaging device or a light-receiving device such as a CCD are classified in the following two kinds in a digital camera.
One is a mechanical shutter for shielding physically radiation of light from a field of a subject. Another is an element shutter or electronic shutter substituted for the mechanical shutter by switching energization of the imaging device.
These shutters of the two kinds are mainly used for the purpose of shielding light in an interlace scan system. This is for a reason that during scanning certain scanning lines of a plurality of scanning lines in order to read out the plurality of scanning lines sequentially, it is necessary to completely shield light from the subject field not to receive pixels constituting the other scanning lines than the above scanned lines, in the interlace scan system.
An amount of receiving light is not different between pixels even though light shielding is not carried out during scanning as the aforementioned interlace scan system in order to read out the entire pixels at once in a progressive scan system, but, there is a case being be shielded by the mechanical shutter in recording a still image because of possibility of generation of a smear by a strong photoelectric during reading out a signal charge.
On the other hand, the electronic shutter causes a signal charge stored in the imaging device to remove in a direction of substrate by means of a Vertical Overflow Drain. With this structure, an exposure can be initiated from a state in which the signal charge of the imaging device becomes zero.
Comparing the electronic shutter with the mechanical shutter from the view of shutter speed, the electronic shutter makes it possible to accomplish a rapid shutter having a speed of over 1/10000 seconds, whereas the maximum of shutter speed of the mechanical shutter is a degree of 1/500 seconds in case of a low cost lens shutter used in a compact camera, because the mechanical shutter requires a time from initiation of shielding to completion of shielding because of a delay on a mechanism.
Therefore, it has been proposed to use a combination of the electronic and mechanical shutters to eliminate the delay of shutter speed of the mechanical shutter while having an advantageous effect thereof.
For example, the initiation of exposure is carried out through an electronic shutter and completion of exposure is carried out through a mechanical shutter, as shown in Japanese Patent Nos. 2624982 and 2624983. In addition, an error due to a delay by the mechanical shutter is compensated by micro-adjustment of the electronic shutter.
However, in the prior art as described above, even though an exposure mode is established by a blanking term or the like being completed, there is a problem that there is a time lag resulting from the micro-adjustment of the electronic shutter until an actual exposure is initiated and therefore it is not possible to photograph an subject moving with a super high speed, for example.
Therefore, in order to resolve such a problem, there is known an imaging apparatus and an imaging method in which an exposure is initiated with a less time lag or without a time lag from a shift to an exposure mode (for example, see Japanese Patent Laid-Open 2002-290823).
In the art of shortening the time lag, when a release shutter button is half-pressed, photometry is carried out through a control part for computing an exposure to determine an exposure time. In addition, the release shutter button is then full-pressed to be switched from a movie mode to an exposure mode by a timing signal generating part.
Consequently, a driver part imparts fixed output pulses of one or more times in the electronic shutter to a photographing part to initiate an exposure from a fixed time. Moreover, a system control part is adapted to control an AE adjusting part to close the mechanical shutter simultaneously with the completion of the exposure time obtained by the photometry.
In this way, in the prior art, the release time lag is minimized by adjustment of the amount of exposure by the mechanical shutter, after the removal of charge from the imaging device is carried out through the electronic shutter with a short time.
However, in this method, an exposure accuracy and maximum in a case that the shutter speed or a time required from the open to the close of the shutter is high depend on a closing accuracy and maximum of the mechanical shutter.
As a result, there is a problem that the maximum of control in a high shutter speed becomes low in the prior art.
In this way, when the shutter speed is high, the exposure time for recording an image becomes short.
It is possible to rapid the exposed time by shifting a period of the electronic shutter or a timing of the mechanical shutter if the exposure time is less than about half of a vertical synchronous signal representing a recording term of one frame.